Method of producing potassium phosphate



Patented May 19, 1931 UNITED TATES OSCAR KASELITZ, OF BERLIN,-GERMA.NY

' METHOD or, PRODUCING POTASSIUM rrcosinrrizrn No Drawing. Application filed. June 17, 1929, Serial No. 371,722, and in Gama November is, 1922?.

,My invention refers to the production of potassium phosphate and more especially mono-potassium phosphate from potassium chloride and phosphoric acid.

It is known that phosphoric acid will replace the hydrochloric acid in potassium chloride, however, this process occurs only at high temperature with such velocity that it is not commercial, the temperatures required leading to the formation of considerable quantities of the undesirable metaphosphate. Moreover, the reaction vessel is quickly destroyed in proportion to the rise in concentration and temperature.

On the other hand, if the operation is carried out with less concentrated phosphoric acid, the hydrochloric acid will escape only very slowly, and a complete conversion into monophosphate cannot be attained.

Contrary to all expectations I have now found that it is possible to carry through this reaction with phosphoric acid of medium concentration and at a temperature which is so low that no metaphosphate worth speaking of is formed. With a quantity, in excess of the molecular, of dilute phosphoric acid of or above 30% concentration, all the chlorine will be expelled under the form of HCl already at 130 C. together with a certain quantity of water, which is evaporated, and in the hot solution crystals of the double-salt KI-I PO 'H PO separate out, but no metaphosphate is formed.

If the operation is carried out under a partial vacuum, the expulsion of H01 is accelerated.

The double-salt separated out from the mother liquor is treated with so much water or mono-potassium phosphate solution that there is obtained solid mono-potassium phosphate and a liquor saturated with monophosphate and the double-salt. The liquor separated from the monophosphate and the mother liquor from the double-salt are used under addition of double-salt, while the monophosphate is treated with water, the resulting liquor being re-used in the decomposition of the double-salt.

I may, however, also add to the hot solution obtained afterexpulsion of the hydrochloric is heated under stirring to about 130 C;

acid so much water or mono-potassium phate solution that after cooling andseparation of mono-potassium phosphate aliquor is' obtained, the composition {of which -cor'responds to the liquor above described, which results in thefldecomposition of the doublesalt. If the process is modified in this manner I avoid the separation of the" double-salt from its motherliquor and the. decomposition in a separate operation. H

l q Example V r starting material shall be used the decomposition liquor obtained on washingthe double-salt, containin 34% 11 1 0 31% .In order to obtain 100 kilograms mono-potassium phosphate, 373 kilograms of this solutionare required,

whichare-prepared by mixing 126.8 kilograms H PO 115.6 kilograms KH PO; and 130.5 kilograms H O. Into this liquor are entered 374 kilograms I-IgPO (100% and 103 kilograms KCl (100%). The mixture The chlorine in the potassium chloride es:- capes as hydrochloric acid and is condensed. Thereupon the reaction mixture cooled downlto 20 0., whereupon the 'double 'saltseparates' out, which is filtered by Suction.

KI-130 1130. and 497 kilograms of a I :There. are obtained 303jkilograms mother liquor containing 47.96% H5190;

25.76% KI-I PO and 2622870: H2O. In order to convert the double-salt into mono-potassium phosphate, it is treated with a'solution saturated with KI-I PO; and having thecomposition: 23.1% vKl-I PO fand 76.9% HO. The decomposition of the quantity of double-salt obtainedrequires 170 kilograms of a liquor prepared by dissolving 39.3 kilograms. KI-I PO in 130.7 kilograms This liquor, is well mixed, bymeans of anagitating' device, with the doublcsalt and the mono-potassium phosphate resulting in the operation is separated by filtration. I thus obtain 100-kilograms mono-potassium phosphate and 37 3 kilograms of a decoin position liquor, which can now be usedas starting material in a new operation.

Various changes may be made in the details vas disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

In the claims aflixed to this specification no selection of any particular modification of the invention is intended to the exclusion of other modifications thereof and the right to subsequently make claim to i any modification not covered by these claims is expressly reserved.

I claim 1. The process of producing mono-potassium phosphate from phosphoric acid and amount of water, in which mono-potassium phosphate is dissolved that, after cooling, the solution obtained according to claim 1 by the decomposition of the double salt is produced as a mother liquor, and decomposing the acid salt resulting on cooling of the solution with so much Water that monophosphate is separated out and a liquor. isiformed which is saturated with monophosphate KKH POQ 'andthe double-salt KH PO 'H PO In testimony whereof I aflix my signature.

OSCAR KASELITZ.

potassium chloride comprising heating potassium chloride with a quantity, in excess of the molecular, of dilutephosphoric acid having a concentration of at least 30% until the hydro- I chlorieacid has been expelled anddecomposthe acidsalt resultingcon cooling of the solution with so much water that monophosphateis separatedout and a liquor is formed which is ,saturated with monophosphate V and the double salt tassiuin chloridewith a quantity, in excess of r themolecular, of dilute phosphoric acid until ithe hydrochloric acid has been expelled, decomposing the hot solution, after the expulsionofi the hydrochloric acid, with; such an amount of ,water that,, after cooling, the .solution obtained according to claims 1 bythe decomposition v of vthe double-salt is produced as a; motherg liquor, and decomposing. the acid salt resulting on cooling ofthe solution withso much water that monophosphate is separated out anda liquor is formed which uns tu ate wi imoneph spha (K Z i) doubl'efsalt xn roi-rnroi.

A. The process of producing ;.,Ino1 10, p0 .tassium phosphate from phosphoric acid a zi'p a si chl r d i omp i ie ahe t e potassium chloride, withv a xp antity in excess iq l hs m le ula O di u Phosp o i ci A bi Q h 1 YdrOQ Qa d ha b n e p l ed, decomposing-the hot solutio nx after; the exbpnlsie lefth yd chlo ic a idm cthsuch an EHO 

